1. Field of the Invention
The present invention relates to gyroscopes and more particularly to a permanent magnet, two degree of freedom, gyroscope which utilizes two optical sensors for obtaining angular displacement information about two axes and rotor pole location information for commutation.
2. Description of the Prior Art
Permanent magnet motors are utilized in inertial gyroscope sensing instruments where optimum efficiency, rate stability and low run up time are required. The drive motors include a two phase stator, permanent magnet rotor and suitable drive circuitry to start, run up and maintain synchronous speed. The rotor is supported by a hydrodynamic bearing wherein the spinning rotor supplies the pressurized fluid for the bearing. In the prior art, permanent magnet motor staring is implemented, without feedback, in an open loop manner. Without position feedback wheel starting characteristics are indeterminate and a no start condition could result under adverse environmental conditions. In the prior art driving and starting of the motor is achieved with a ramped increasing frequency two phase drive. At a suitable rotational speed, typically five to ten percent of synchronous speed, the windings of one phase are open and its back EMF provides a signal indicative of rotor position and speed. The other phase winding is energized, as a function of the back EMF signal, after the back EMF signal has been processed by suitable drive electronics.
During normal operation, after starting the permanent magnet motor is operated single phase. A permanent magnet two degree of freedom gyroscope, utilizing a single rotor, provides the same information as two single axis gyros. The single rotor, requiring only a single set of motor drive electronics, allows two axes of information to be contained in a compact package thus making it desirable in applications where size and weight are prime concerns. In addition to the sensors required for starting and running, prior art permanent magnet two degree of freedom gyros typically require two pickoff sensors to extract angular displacement information about the yaw and pitch gimbal attitudes. Each sensor contributes to the overall gyro size, cost and harnessing complexity and it is therefore desirable to use as few sensors as possible without sacrificing any information.
The present invention eliminates the start/restart electronics and continuously operates the permanent magnet gyro motor in a two-phase, closed loop, drive mode. The location of the rotor poles is determined by two optical sensors which are also utilized for sensing angular displacement about two axes. Both drive phases are available at all times to be driven for maximum torque.